The Justice Department "found no evidence" that Attorney General Eric Holder knew before January 2011 of the "inappropriate tactics" used in Fast and Furious gun-walking scandal, according to a report released Wednesday by the Office of the Inspector General.

We're still going through the 471-page report, but there's at least one reason within the report that raises doubt in its conclusion.

"Gun-walking" or "letting guns walk" was a tactic of the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) whereby agents purposely allowed licensed firearms dealers to sell U.S. weapons to illegal straw buyers in the hopes of tracking those weapons to Mexican drug cartel leaders and arresting them.

The Fast and Furious operation (2009-2011) was the largest of several gun-walking operations—including Operation Wide Receiver (2006-8)—that took place under a broader initiative known as Project Gunrunner (2006-2011), which was intended to reduce the flow of firearms into Mexico.

One reason to doubt the new report is that it ostensibly found no evidence that Michael Mukasey, Attorney General from November 2007 to January 2009, was "made aware of Operation Wide Receiver, or of the investigative tactics that were employed by ATF during that investigation."

However, a Justice Department memo to Mukasey from Nov. 16, 2007, outlines failed attempts by federal agents to track walked guns across the border into Mexico.

AsAP reported last year, the memo "marks the first known instance of an attorney general being given information about the tactic known as 'gun-walking.'"

The memo goes on to state that while Wide Receiver was unsuccessful, the ATF "would like to expand the possibility of such joint investigations and controlled deliveries."

Wide Receiver monitored the sale of about 450 guns and lost almost all of them while Fast and Furious monitored the sale of more than 2,000 firearms, of which nearly 700 were recovered as of October 2011.

The obvious question:Why does the new Inspector General report contradict the earlier Justice Department memo?

A follow-up question:If the earlier Justice Department memo is to believed, wouldn't Holder, who followed Mukasey as Attorney General, also be informed of the "inappropriate tactics" used in gun-walking operations when he took office?

The operations of Project Gunrunner became controversial when weapons from Fast and Furious were recovered from the Arizona desert where U.S. Border Patrol Agent Brian Terry died in a shootout with cartel members on December 14, 2010.

The AP story noted that, according to ATF data, 94,000 weapons were recovered in Mexico from 2006 to 2011 with 64,000 of them traced to the United States.